The invention relates to compressor blades and, in particular, to leading edge treatments to increase blade tolerance to erosion.
Water is sprayed in a compressor to wash the blades and improve performance of the compressor. Water washes are used to clean the compressor flow path especially in large industrial gas turbines, such as those used by utilities to generate electricity. Water is sprayed directly into the inlet to the compressor uniformly across the flow path.
Water sprayed on the hub hits the blades of the first stage of the compressor. These rotating first stage blades shower water radially outward into the flow path of the compressor. The water is carried by the compressor air through the compressor vanes and blades. The water cleans the compressor and vane surfaces. However, the impact of the water on the first stage blades tends to erode the leading edge of those blades especially at their roots, which is where the blade airfoil attaches to the blade platform.
Erosion can pit, crevice or otherwise deform the leading edge surface of the blade. Erosion often starts with an incubation period during which the blade, e.g., a new blade, is pitted and crevices form in the blade leading edge. As erosion continues, the population of pits and crevices increases and they deepen into the blade.
The blade is under tremendous stress due to centrifugal forces and vibration due to the airflow and the compressor machine. These stresses tear at the pit and crevices and lead to a high cycle fatigue (HCF) crack in the blade. Once a crack develops, the high steady state stresses due to the centrifugal forces that act on a blade and the normal vibratory stresses on the blade can cause the crack to propagate through the blade and eventually cause the blade to fail. A cracked blade can fail catastrophically by breaking into pieces that flow downstream through the compressor and cause extensive damage to other blades and the rotor. Accordingly, there is a long felt need to reduce the potential of cracks forming in compressor blades due to blade erosion.